Worldwide revenue from pornography amounted to at least $97 billion in 2006, according to the Internet site TopTenReviews.com. In a review of software filters, the website claimed that more than $3 million is spent on pornography every second. Although most pornographic films and photographs available on the Internet are produced in the U.S., the Chinese were the biggest buyers, spending $27.4 billion last year, the website said. The U.S. was fourth on the list with $13.3 billion, followed by South Korea, with 25.7 billion, and Japan, with $20 billion. The website surveyed only the top 20 countries.